1. Field of the Invention
The present invention relates to a structure in which thin-film transistors (TFTs) are integrated with a ceramic device or with a ferrite device. The invention disclosed herein can be used in a small-sized, lightweight intelligent terminal typified by a mobile phone, for example.
2. Description of the Prior Art
In recent years, research has been carried out on techniques for fabricating transistors, using a thin silicon film formed on a substrate of quartz or glass. Some of them have been commercialized. These transistors are known as thin-film transistors (TFTs).
The main purpose of the research into TFTs is to use them in liquid crystal displays. Such a liquid crystal display has a number of pixels arranged in rows and columns. TFTs are disposed as switching devices at the locations of the pixels. Electric charge held on pixel electrodes is controlled by the TFTs.
A still advanced structure that is known has a peripheral driver circuit consisting of TFTs, similarly to an active matrix circuit. This configuration achieves ever larger scales of integration.
Furthermore, it is considered to construct from TFTs circuits for handling graphics information and for exchanging information with the outside, as well as the peripheral driver circuit. Thus, the whole structure is systematized.
Recently, intelligent terminals having various information-processing functions have attracted attention. These intelligent terminals are also termed mobile computers and have various functions such as communications functions (such as fax and telephone), information storage functions, and arithmetical processing functions.
The intelligent terminals described above are required to be small and light enough to provide portability. In addition, they are required to have a thin-film display (also known as a flat panel display) to handle graphics information. Of course, an intelligent terminal needs a circuit for exchanging information with an external device.
It would be inevitable that more cordless information-transmitting means are used. In particular, there is a demand for a function of exchanging information, using electromagnetic waves in the GHz band or higher permitting exchange of high-density information. Accordingly, the intelligent terminal described above must be a small-sized, lightweight device incorporating a radio-frequency circuit capable of sending and receiving electromagnetic waves in the GHz band.
Generally, this radio-frequency circuit comprises transistors integrated with a filter element (such as an inductor or capacitor in chip form or an SAW device). These transistors use a single-crystal silicon wafer or compound semiconductors. In the future, more functions will be required. Furthermore, smaller size, reduced weight, and lower cost will be necessitated. In spite of these technical trends, it is now difficult to increase the device density further.
It is an object of the present invention to provide a novel device in which a radio-frequency circuit capable of handling radio frequencies in the GHz band is integrated with other component.
The present invention provides a device comprising a substrate having TFTs fabricated on an insulating surface, terminals connected with the TFTs and extending through the substrate, and a laminated device connected with the terminals.
Also, the invention provides a device comprising a first substrate having TFTs fabricated on an insulating surface and a second substrate having a laminated device. These first and second substrates are bonded together. Terminals extend through the first substrate to connect the TFTs with the laminated device.
The laminated device can consist of layers of magnetic or dielectric materials. One example of magnetic material is a ferrite that is one kind of ceramic material.
In one preferred embodiment of the invention, the above-described radio-frequency circuit is made up of TFTs, and the laminated device forms a filter circuit.
Heat generated by the TFTs can be effectively radiated by forming a heat-radiating layer on the first substrate. Preferably, the heat-radiating layer is made of a material of high thermal conductivity such as aluminum nitride.
Moreover, the invention provides a device comprising a first substrate and a second substrate that are bonded together. The first substrate has an insulating substrate on which TFTs are fabricated. Passive components are fabricated on the second substrate. Terminals extend through the first substrate to connect the TFTs with the passive components.
The heat-radiating layer can be made of aluminum nitride (AlN). Besides, the layer can be made of aluminum nitride to which oxygen is added, (AlON). In addition, the layer can be made of crystalline compounds of Si, Al, O, and N that are collectively known as SIALON. Further, the layer can be made of AlONC. These materials are effective in relieving the stress between the substrate and the device and controlling the thermal conductivity, and have various features including electrical insulation, high thermal conductivity, heat resistance, and optical transparency.
In addition, the invention provides a device comprising first and second substrates bonded together. A circuit is fabricated from TFTs on the bonded surface of the first substrate. Another circuit is fabricated from a ceramic device on the bonded surface of the second substrate. These two circuits are connected together.
In this configuration, heat generated by the TFTs can be effectively radiated by a heat-radiating layer formed on the first substrate.
Also, the ceramic device can be fabricated, using a dielectric or magnetic material. The ceramic device can be fabricated, using a ferrite.
The heat-radiating layer can be made of aluminum nitride (AlN). Besides, the layer can be made of aluminum nitride to which oxygen is added, or AlON. In addition, the layer can be made of crystalline compounds of Si, Al, O, and N that are collectively known as SIALON. Further, the layer can be made of AlONC.
These materials are effective in relieving the stress between the substrate and the device and controlling the thermal conductivity, and have various features including electrical insulation, high thermal conductivity, heat resistance, and optical transparency.